1. Field of the Invention
The present invention generally relates to a display device. More particularly, the present invention relates to a reflective type liquid crystal panel.
2. Description of Related Art
The liquid crystal on silicon (LCOS) panel is in fact a silicon wafer back panel, by using MOS transistors in place of the thin film transistors used in the conventional liquid crystal panels. Generally, the LCOS panel has two basic types: transmissive and reflective. Nevertheless, the most research and development work is centered on the reflective type LCOS panel. The pixel electrodes of the reflective type LCOS panel are made of metal materials. Moreover, because the metal pixel electrodes mostly cover the pixel regions, especially the MOS transistors, the LCOS panel is superior in image display compared with conventional liquid crystal panels.
FIG. 1 schematically illustrates a circuit layout of a pixel in a conventional reflective type LCOS panel. As shown in FIG. 1, the storage capacitor 120 and the LC capacitor 130 can be charged to a voltage by controlling the MOS transistor 110, and the liquid crystal molecules in the LC capacitor 130 are aligned along a specific direction according to the voltage. Furthermore, the storage capacitor 120 is used for maintaining the voltage of the LC capacitor 130 during a frame time for superior displaying uniformity. Because the MOS transistor 110 is made from semiconductor material, leakage currents induced by light entering the LCOS panel, especially the one occurring at the drain terminal 116 of the MOS transistor 110, may lead to a descent in the voltage of the storage capacitor 120, and the displaying uniformity of the LCOS panel goes inferior.
Accordingly, LCOS panels coming with light shielding function are brought out. FIG. 2 shows a schematic cross-sectional view of a conventional reflective type LCOS panel fabricated from a typical 1P3M (single polysilicon layer and three metal layers) wafer process. As shown in FIG. 2, the LCOS panel 200 comprises a silicon substrate 210, a liquid crystal layer 220, and a glass substrate 230. MOS transistors 212 corresponding to different pixel regions 202 are fabricated in the silicon substrate 210 respectively. Reflective pixel electrodes 250 are provided in their corresponding pixel regions 202 with light transmissive regions 252 being located between the reflective pixel electrodes 250. A routing metal layer 214 to form mutually-orthogonal row and column lines (not shown in FIG. 2), which may be electrically connected to the gate, source and drain terminals (not shown in FIG. 2) of the MOS transistors 212, is formed above the silicon substrate 210. In addition, a light shielding metal layer 216 is provided beneath the light transmissive regions 252 between the reflective pixel electrodes 250 and the routing metal layer 214 to prevent light entering the LCOS panel 200 through the transmissive regions 252 from reaching the silicon substrate 210.
However, it is noted that a separated light shielding metal layer 216 is required for the reflective pixel electrodes 250 to be electrically connected with the routing metal layer 214. Thus, the light entering the LCOS panel 200 through the separated light shielding metal layer 216 may still reach the silicon substrate 210, and the induced leakage current can not be exactly eliminated. Furthermore, high pattern density of the light shielding metal layer 216 may lead to unexpected mechanism effects such as stress concentration or poor wafer flatness.